This week, Chinese President Xi Jinping is making his first official visit to the US. It takes place against a background of accusations flung by both the US and China over state-backed hacking.
On Monday this week, a US national security adviser warned China that the hacking must stop and said it put an “enormous strain” on the relationship between the two nations.
How has China responded to the accusations?
It has denied everything.
In an interview with the Wall Street Journal, Mr Xi said: “The Chinese government does not engage in theft of commercial secrets in any form, nor does it encourage or support Chinese companies to engage in such practices in any way.”
He went on to say that cyber-theft of industrial secrets was a crime as were hack attacks against government networks.
Both should be punished according to “law and relevant international conventions”.
The president’s comments echo many others made by Chinese state spokespeople over the years who regularly dispute the accusations levelled at them.
Are China’s denials credible?
Not to Kevin Mandia, boss of security firm FireEye, who has spent 20 years helping the US government and its contractors clear up after data breaches and work out who did them.
“It’s them and we know it’s them,” he said bluntly, when asked if China hacked Western firms.
How can he be sure?
He based his conclusion on 20 years of investigations that have catalogued thousands of attacks – 226 in 2014 alone. Forensic analysis of these has, he said, led FireEye to conclude that the Chinese state is behind them.
The company has evidence about net addresses, net domains, attack techniques, tools and character sets used in the attacks.
It has built up a log of 15-20 separate telltale signs that identify each of the military groups in China behind the breaches and intrusions.
And, he said, the attacks are not random. They are well-organised campaigns that go after specific industries seeking specific data.